The present invention pertains to devices used for delivering a measured volume of powder from a hopper, and more particularly pertains to a powder feeder or meter which can be used to deliver measured amounts of powder as desired and is particularly effective with thermosetting resinous powders.
Powder feeders and meters are used to measure the amount of powder being processed through a device. The rate of flow can be affected by such variables as humidity, particle size particle shape, density, material cohesiveness, and chemical composition. These alone or in combination at times render existing powder feeders useless or troublesome.
Because of their chemical composition, some resinous powders with catalysts have a tendency to undergo cross-linking when very slight amounts of mechanical work or low level heating are acting upon them. Either of these conditions can cause a catalyst-resin reaction, which is exothermic, and result in sintering or agglomeration of these powder particles rendering them unflowable and/or retarding their usefulness in coating applications. Variations in the rate of flow can cause excessive rejects, wasted powder, and extra costs attributable to reclaiming excess powder.
Some previous precision powder feeding and/or measuring devices employ a screw type conveyor much like the shaft of an auger to meter the powder from a hopper to the application device. This method causes mechanical work to be done on the powder due to pressure being exerted by the screw in moving the powder. Any close tolerance moving surfaces, screw to wall clearances, for example, bearings, or seals can cause sintering or agglomeration as above-mentioned with some resinous powders. None of these feeders or meters can be used in a powder coating application in which the excess powder is recycled through the feeder a second time without further degrading the powder's flowability and subsequent functional characteristics.
Another problem is that the most precise powder meters and/or feeders available heretofore, namely the screw type feeders, are only capable of feeding a single output or applicator. Therefore, size limitations and cost become important considerations in setting up a powder meter, conveyor and applicator.
It is therefore highly desirable to provide an improved powder feeder.
It is also highly desirable to provide an improved powder feeder which can precisely meter measured volumes of powder per unit of time.
It is also highly desirable to provide an improved powder feeder whose output can be varied over its operating range with one nearly linear controlling variable.
It is also highly desirable to provide an improved powder feeder which can precisely meter powder without imparting mechanical work on the powder.
It is also highly desirable to provide an improved powder feeder which can precisely meter resinous powder without producing low-level heating effects which cause agglomeration and/or pre-application sintering.
It is also highly desirable to provide an improved powder feeder which is capable of metering reclaimed powder.
It is also highly desirable to provide an improved powder feeder which precisely meters measured volumes of powder and is capable of feeding one or a plurality of applicators.
It is also highly desirable to provide an improved powder feeder which precisely meters measured volumes of powder and is less expensive to manufacture, maintain, and install.
It is finally highly desirable to provide an improved powder feeder which meets all of the above desired features.